To enable a driver of a vehicle to operate a brake input element of a brake system, for example a brake pedal, comfortably, a brake system generally includes a brake booster. The brake system with a brake booster is often referred to as a brake-boosted brake system.
A brake booster is configured to provide an assistance force which, in addition to a driver braking force exerted on the brake input element by the driver, brings about braking of at least one wheel. Suitable brake boosters are described, for example, in German Patent Application Nos. DE 10 2005 024 577 A1, DE 10057 557 A1 and DE 103 27 553 A1.
FIGS. 1A and 1B show schematic illustrations to explain a mode of operation of a conventional brake booster.
The brake system shown partially schematically in FIG. 1A has a brake input element 10 which is provided, for example, in the form of a brake pedal. By operating brake input element 10 the driver is able to apply a driver braking force Ff and a first adjustment travel s1 to a transmitting component of the brake system, for example to an input piston 12 (see equivalent circuit diagram of FIG. 1B). In addition, driver braking force Ff may be sensed by a brake input element sensor system (not shown). The brake input element sensor system includes, for example, a force sensor for measuring driver braking force Ff and/or a travel sensor for ascertaining first adjustment travel s1 of an adjustable component of brake input element 10.
The brake system additionally includes a brake booster 14. Brake booster 14 is configured to provide an assistance force Fu so that the driver does not have to apply the force required to brake his vehicle entirely in the form of a driver braking force Ff. Assistance force Fu provided by brake booster 14 may, for example, be a function of driver braking force Ff.
Brake input element 10 and brake booster 14 are arranged in the brake system in such a way that at least driver braking force Ff and assistance force Fu produce a total braking force Fg. Total braking force Fg may, however, also include at least one further force. For example, brake booster 14 transmits assistance force Fu and a second adjustment travel s2 to an assistance piston 16 which is coupled, together with input piston 12, to a force introduction element, such as the reaction disk 18 shown. In the equivalent circuit diagram of FIG. 1B, input piston 12 acts on a first point P1 and assistance piston 16 acts on a second point P2 of reaction disk 18. Points P1 and P2 may correspond to areas. For example, point P2 corresponds to an annular area in the case of a tubular assistance piston 16.
In that manner it is possible for total braking force Fg and a third adjustment travel s3 to be transmitted to a component disposed on the output side of the force introduction element, for example to output piston 20. In that arrangement, output piston 20 touches reaction disk 18 at a third point P3, or at a corresponding area.
A quotient x indicates the ratio of a first distance between points P2 and P3 and a second distance between points P3 and P1. In the case of an elastic reaction disk 18, reaction disk 18 is deformed at a driver braking force of Ff≠0 and/or at an assistance force of Fu≠0 (not illustrated in FIG. 1B). The deformability of reaction disk 18 may be given as elasticity e.
Output piston 20 is coupled to an adjustable component 21 of a master brake cylinder 22. A brake circuit (not shown) filled with a brake medium and having at least one wheel brake cylinder is connected to master brake cylinder 22. By changing a brake pressure in the at least one wheel brake cylinder, it is possible to exert a hydraulic braking torque corresponding to total braking force Fg, or a corresponding hydraulic braking force, on the at least one associated wheel.
German Patent Application No. DE 10 2007 030 441 A1 furthermore describes a motor vehicle brake system with a generator, and a corresponding method for operating a brake system having a generator. If, in addition to a hydraulic braking torque, a generator braking torque acts on at least one wheel, a simulation unit is to be actuated in such a way that a volume of hydraulic fluid corresponding to the generator braking torque is taken out of the brake system and temporarily stored in at least one accumulator chamber of the simulation unit in order to reduce the hydraulic braking torque by the generator braking torque. Correspondingly, on deactivation of the generator braking torque, the volume of hydraulic fluid is to be returned to the hydraulic brake system for an increase in the hydraulic braking torque.